Separation of nickel and cobalt



Dec. 27, 1955 G. F. VAN HARE, JR., ETAL 2,728,635

SEPARATION 0F NICKEL AND COBALT Filed Sept. l5, 1951 I I I I I I I i I II I I I I I I I N f ff .m il mf .nc of M IIZ n N W m A M M 0 c. v r f @yf 0 x@ I 5 0/ 5.. v/Af n a N M` ab M f M P W i. m M N P 5 .um V 7 f .f mm W. N F W VM 0 i I w of vm DL cr f um W M .I6 www N N X 5 i O f W U oH.- a w N M w W C 0 ,m e m M 0 +.o1 a o4 f fr P an, W P p 5w )E o y oMJA# IIIIII IIWA, C5 C f( lNvEN-roRs Grandi A'. VAI/V #Ang/, WQL TER ffMc CON/ ATTORN EY United States Patent() y a c 2,728,636

l sEPARATroN or NICKEL AND COBALT Application September 13, 1951, SerialNo. 246,404

2 Claims. (Cl. 23-117) This invention relates to the hydrometallurgy ofnickel and cobalt. More specilically, it is concerned with theseparation ,of these metals `from one another when both are contained inthe same solution. Still more specifically, it involves a new method ofprecipitating a substantially nickel-free cobalt product from solutionscontaining the mixed soluble salts of both metals in any reasonableproportion.

Nickel and cobalt metals, and their naturally occurring minerals, arevery similar to one another in both physical and, chemical properties.Moreover, both metals generally occur together in their natural depositsand cannot Vbe separated by ore dressing methods. For these reasons,both metals are generally present, in varying amounts, in all solutionsthat result from any type of ,leaching of either` nickel or cobaltnatural or intermediate products.

In the conventional metallurgy of either nickel` or cobalt, the presenceof relatively large. quantities of the minor metal in the ores andconcentrates of the major one has always'been a serious and diflicultproblem. This problem has never heretofore been solved in a satisfactorymanner whereby the bulk of each metal may be recovered in a separate,relatively pure product. In present practice, when small amounts ofcobalt are pres.- ent in nickel concentrates, most of that cobalt isdiscarded in the slag from nickel smelting. The remainder is sold in thenickel bullion or cathodes as nickel` metal. Very little is recoveredand' sold as cobalt metal, primarily because the cost. of separation, bypresent methods, is at least as great as the additional value of thecobalt metal.

When small amounts of nickel are present in cobalt concentrates, and,therefore, in the cobalt solutions, this nickel is generally eitherdiscarded at considerable cost, or is recovered with the cobalt. In thelatter case,4 the nickelbecomes an impurity in the cobalt metal, and

' the producer is generally not paid for it. In' some cases,

certain nickel and cobalt mixed metals are marketable as such, butusually at a price below the value of the pure metals in separateproducts.

It is, therefore, apparent that a process for the cicient separation ofcobalt and nickel into separate products would be very useful in bothnickel and cobalt conventional metallurgy.

A large numberv of such processes have been either proposed or used forthe treatment of cobalt and nickel electrolytes. Most of these processesinvolve the simul taneous or successive selective oxidation of .cobaltto cobaltic hydroxide, while the electrolyte is being partiallyneutralized with an alkali. Cobalt is slightly easier to oxidize to thetrivalent state than nickel under certainv conditions, and theyresulting cobaltic salt will hydrolyze and precipitate from a slightlymore acidic solution than will the parallel nickel hydroxide.

One process which uses this principle employs sodium or potassiumperchlorate as .an oxidizing agent, and lime plus soda ash to neutralizethe solution. The resulting Vice Vprecipitate is a mixture .of gypsum,limerock, and a cobalt-enriched hydroxide solid which may be treated forthe removal of cobalt and nickel. The liquid is then generally suitablefor electrolytic precipitation of at least part of the contained nickel.It may have to be recycled for a second or third cobalt removal beforeall of the nickel can be stripped from it.

Another variation of the above type of process involves the oxidation ofcobalt with chlorine gas, which forms HC1. plus HOCl in solution,` andthe neutralization of the solution with soda ash. This process resultsin the precipitation of a mixture of cobalt and nickel hydroxides, andthe liquor may be made free of cobalt. The liquor is then ready forelectrolysis or any other type of nickel recovery. The residue must beretreated. Various recycling systems have been Worked out to improve theseparation of nickel and cobalt in `each of the above processes. i

An additionalacid` liquor separation process involves the electrolyticoxidation of cobalt to the higher state.

rfhisr is followed by a chemical precipitation of the cobalt as a mixedhydroxide with nickel. The mixed hydroxide is removed Vby filtration,and then. a second electrolysis is conducted for the recovery ofelectrolytic nickel. When the cobalt ratio. again becomes high, thesolution is either returned to the leaching or to the cobalt oxidationsteps of therprocess.` p

There are several methods of separating nickel and cobalt from ammoniumcarbonate leach liquors. Most of these involve fractional distillationof the ammonium carbonate. The mother liquor, at diiferent stages in theprocess, thereby becomes concentrated with either nickel or cobalt. Thisliquor may then be removed and treated separately. The residue may beredissolved. and retreated separately.

Conventional processes for the production of nickel or cobalt result in.products containing relatively large amounts of the other metalrespectively. This relatively poor separation is probably due, in partat least, to the fact that the separations are made .by theprecipitation of hydroxide. or basic carbonate solids. These solidsalways occlude or adsorb large quantities of the solution from whichthey are precipitated. This adsorption or occlusion effect alsogenerally makes the filtration of hydroxides dithcult to performeciently.

Most of the conventional acid separation processes require the use oflarge quantities of chemical reagents, manyof which arenon-regenerative. This creates a disposal problem. Those processes whichdo not require large quantities of chemical reagents either result inhigh metal losses or are extremely complicated in the amount ofprocessing that is required to achieve minimum metallurgical results.

It is, therefore, an object of this invention to provide an `improvedmethod for the separation of cobalt from nickel. lt is a further objectof this invention to provide a method of processing cobalt and nickelvcontaining `ores or minerals concentrates, whereby these metals may berecovered in a percentagewise amount and at an economy bothV heretoforeunrealized. Such a process should involve the use of only commonlyavailable chemical reagents. The process shouldA also involve the use ofonly those chemical reagents which may be either regenerated orsold as avaluable by-product of the process.

Surprisingly, the desired objects of. this invention have been achievedin an amazingly elective manner. in general, the over-all process issurprisingly simple. It requires, first adjusting theanion ratio of thesolution of the metals so as to provide a concentration of the anionsufficient to form a cobaltic salt from the cobalt present in thesolution. p

This solution is then saturated withl ammonia, to form Patented Dec. 27,1,9555

complex amine salts of the metals. It is pressurized, heated to about250 F. and subjected to oxidation with a substantially sulfur-free,oxidizing gas. Under the proper conditions a yellow-orange crystallinecobaltic ammine salt virtually free of nickel will be precipitated,while the nickel will remain in the solution, presumably in its originalform.

The resulting slurry is ltered Vand the presscake washed. The presscake,comprising the cobaltic ammine as a crystalline salt which is virtuallynon-soluble in cold water, may be easily washed substantially free ofnickel salts, It may be further processed by known methods to recoverpure cobalt metal. The filtrate is not necessarily cobaltfree, but mayhave to be subjected to a second treatment with ammonia. This secondtreatment will remove the remaining cobalt as anV intermediate cobaltproduct, and will purify the nickel solution so that it can be used forI the direct production of pure nickel. The intermediate cobalt productcan be recycled to the first step of the process or can be used to makea mixed metal product if desired.

This invention provides an etfective separation of nickel and cobalt,irrespective of the original ratio of either metal in the solution. Itwill also be noted that this invention enables the almost completerecovery of both metals from virtually any type of salt solution.

Although the description of the flow diagram will be applied to asulfate solution of cobalt and nickel, it should be understood that theinvention is just as applicable to other salt solutions of the metals.

The general procedure of this invention may be more fully described inconjunction with the accompanying drawing'. This latter constitutes asimplified flow diagram illustrating the principal steps of the presentprocess.

With reference to the flow diagram it will be seen that the rst step ofthe process involves the optional addition of ammonium sulfate to thesolution comprising Ni and Co salts. This permits adjustment of theanion ratio, if it does not already exist, so as to provide at leastsufficient anions, in this case SO4=, to satisfy each mol of cobalt inits trivalent state, and each mol of nickel in its bivalent state.Ammonia is then added to saturate the solution. The solution is thenpressurized and heated, and subjected to oxidation. Heating is conductedso as to raise the temperature of the solution to about 150-450 F.,preferably about 200-350 F. At lower temperatures the reaction is tooslow, at higher temperaturesthe total pressure becomes too great to behandled in conventional equipment. Moreover, at too high temperaturesthe nickel is also oxidized. Suicient pressure should be used to keepthe major portion of the ammonia in solution. A substantiallysulfur-free, oxygen-bearing, oxidizing gas is injected into the vesselto oxidize the cobalt from the cobaltous to the cobaltic state.

The above procedure results in the oxidation of the cobalt to thetrivalent state and the formation of a cobaltic ammine sulfate whichprecipitates as an orange colored crystalline product. Under the properoperating conditions, nickel is not believed to be oxidized. If it is,however, itrernains in solution. The precipitate will contain up toabout 85% or more of the cobalt originally in the solution, dependingupon the cobalt to nickel concentration, and practically none of thenickel. This salt has a dry analysis which corresponds approximately tothe formula [Co(NH3)6]2(SO4)3'2H2O. It is only slightly soluble in thestrongly ammoniacal treating solution, but more soluble in hot water,dilute ammonium hydroxide and dilute acids. It is easily filterable andhas no tendency to adsorb solutions.

After oxidation, the resultant slurry is cooled and the solidscollected, usually by liltration as shown in the drawing. If the processhas been properly conducted, the resulting presscake, as indicatedabove, will contain as the cobaltic ammine sulfate up to at leastabout85% ofA the wbaltortiginally iasvlutivn, .but Practically none annesse,f

of the nickel. The collected solids are washed, Washings being recycledas shown, and then sent to a recovery system for recovery of the puremetal cobalt. This recovery system may involve any suitable method, theexact nature of which forms no part of this invention.

The residual liquor contains substantially all of the nickel and theresidue of the original cobalt. If so desired, this liquor may be sentdirectly, as shown by the alternative ow line, to a nickel recoverysystem. Recovery per se of the nickel metal forms no part of thisinvention. Accordingly, any suitable method for the recovery thereof maybe employed.

As shown in the drawing, rather than being sent directly to a nickelrecovery system, the filtrate may be further treated to remove theremaining cobalt, thus leaving a substantially cobalt free nickelltrate. This treatment of the filtrate comprises another addition ofammonia to further decrease the solubility of the cobaltic salt.Treatment is continued until all remaining cobalt is precipitated as thecobaltic ammine. Included in this precipitate will be a part of thenickel, probably as the nickelic ammine.

As shown, the mixed metal precipitate resulting from the secondtreatment with ammonia is collected as before by being washed andltered. Washings may be recycled, usually to the first solids removalstep. The substantially cobalt free nickel filtrate is sent to thenickel recovery system.

Two ows exist for disposing of the mixed metals presscake. One of these,as shown, involves the recycling thereof to the oxidation step for afurther separation. Alternatively, the presscake may be sent to a mixedmetals recovery system for recovery of a mixed metals product. As withthe nickel and cobalt recovery systems, the exact nature of the mixedmetals recovery system forms no part of this invention.

' Shown on the ow diagram are two other alternative ows. Immediatelyfollowing the oxidation step is shown theaddition of ammonia. Partialaddition, at this point, ofthe required amount of ammonia allows theaddition of less in the oxidation step. This permits the use of lowertotal pressures during oxidation. Moreover, it

constitutes a more accurate control of the ammonia addition.

The other alternative ow is an oxidation treatment at the second solidsprecipitation. Such a step may be necessary to insure complete oxidationof the cobalt to the trivalent state. Whether this step is warrantedwill depend upon the extent of the original oxidation. Moreover, thisstep may be employed alone to complete the precipitation of the cobaltprovided suicient ammonia was initially added.v Generally, however,initial ammonia addition will be such that the second oxidation step, ifrequired, will not be used alone but in combination with a furthertreatment with ammonia.

Concerning the operation of the process, certain factors should beconsidered. The preferred operating temperature range is between about200 to 350 F. Much higher operating temperatures may be employed but theuse of such will necessitate the use of equipment adapted to withstandthe correspondingly higher pressure. Moreover, at these highertemperatures, oxidation of the nickel increases. For these reasons, itis desirable, although not essential, to operate within the preferredrange mentioned.

There is no specific range of total operating pressure conditions.However, a total pressure should be maintained at least equivalent tothe vapor pressure of the solution. Likewise, there is'no specific rangeof O2 partial pressure. The partial pressure of O2, however, should besuch as to at least insure oxidation of the equivalent amount of cobaltfrom the cobaltous to the cobaltic stage.

The oxidizing agent may be any oxygen containing oxidizing gas. Air,oxygen enriched air, or oxygen may be satisfactorily employed. It isessential, however, that dilution increases.

avancee" to prevent the formation of the metal suldes.

Suflicient salt-forming anions must be present inthe i solution toprecipitate the cobaltic ammine complex in the form of a salt. The anionconcentration, therefore, must be at least suflieient to permitformation of the cobaltic ammine salt as well asthe nickelous amminesalt. Accordingly, the anion ratio should be at least equivalent to thesum of three chemical equivalents for each mol of ,cobalt and V twochemical equivalents for each mol of nickel. Presence of suiiicientsaltfforming anions also functions as a bulfer with respect to theprecipitation of the cobalt as ahydroxide. Y '1 i Since cobalt in thepresent invention is precipitated as a cobaltic ammine salt, it isessential that the ammonia concentration be such as to permit formationof the ammine. Any ammonia in excess to this servesr to saturate thewater and decrease the solubility of the cobaltic ammine. The totalconcentration of ammonia necessary is a function of the waterpresent andwill increaseas the In all cases, however, the ammonia to water ratiorequired will be substantially constant.

The following examples further illustrate the invention:

Example I A leach liquor is prepared by dissolving approximately equalquantities of reagent grade nickel and cobalt sulfates in water andadjusting withv ammonium sulfate and aqua ammonia until a solution ofthe following composition is obtained is necessary to provide enoughsulfate ions for the cobaltic salt, as well as for the soluble nickeloussalt.

The solution is charged to an agitated pressure vessel and heated toapproximately 250 F., at which temperature compressed oxygen is forcedinto the body of the liquid until the total pressure reachesapproximately 250 p Thee conditions of temperature, pressure andagitation are held constant for approximately one hour. The contents arethen removed, filtered and the residue washed. The orange coloredcrystalline residue obtained analyzes Vapproximately 85.6% of the cobaltin the feed solution but only 0.6% of the nickel. This precipitate,although produced from a solution containing equal quantities of eachmetal, contains a ratio of cobalt to nickel in excess of 142 to l. Thefiltrate containing the remaining cobalt plus most of the originalnickel is further oxidized under conditions as above but for a shorterperiod of time. The resulting precipitate contains virtually all of theremaining cobalt in the solution plus about 12.4% of the nickel. Thesecond filtrate now contains approximately 86.4% of the nickel andvirtually none of the cobalt.

Example Il The feed liquor of this example is obtained from a leachingtreatment of a Missouri nickel-cobalt ore concentrate containing a moleratio of approximately Ni to 4 Co. Since excess sulfuric acid is alsopresent in the leach liquor, the adjustment thereof requires only theaddition of am monia in the properfratio,` producing a solution of thefollowing composition:

is required to provide enough sulfate ionsfor the cobaltic salt, as wellasfor the soluble nickelous salt. l

Oxidation, conducted similarly to that in Example I,

produces an orange crystalline residue which contains 82.4% of thecobalt in the original solution and onlyf 0.1%

ofthe. nickel. Ratio of Vcobalt to nickel n'this residue isapproximately 380 to l. The filtrate is treated with NH3 gas whichprecipitates virtually all of the remaining cobalt as well as about 8.9%of the nickel. The second filtrate contains about of the nickeloriginally in solution but none of the cobalt. The mixed residue is4recycled to the adjustment operation.

Example 111 The feed liquor of this example is obtained from a leach-Aing treatment of an Idaho cobalt-nickel ore concentrate,

which contains a mole ratio of approximately 20 Co to 1 Ni. Excessiveacid in the leach liquor requires the addi tion of lime slurry as wellas aqua ammonia. The calcium sulfate precipitated is removed byfiltration.

The adjusted solution has the following composition:

Cgglitlilon Concentration Mole Ratio Cosol 126.o'gm./1.=0.s15 mol/1-.-.-so4/N1+Co=1.4s

Nrsor 6.7gm./1.=0.043mo1/1 oo/Nl=19.o (NHozsol 54.4 gm./1.=o.412 mol/1NHa/Ni-l-oo=14.4 NH3 210.0 gm./1.=i2.35 mol/1.-.-. A

The ratio SO4/Ni|Co=1.47 is required to provide enough sulfate ions forthe cobaltic salt, as well as for the soluble nickelous salt.

Oxidation is identical to that of Example I and results in an orangecolored precipitate. The cobalt content thereof is 95.3 of the cobalt inthe feed solution, while the nickel content is only 0.1%. Cobalt tonickel ratio in this precipitate is approximately 450 to 1. The filtratefrom the separation of the cobaltic salt is treated with NH3 gas.Virtually all of the remaining cobalt is precipitated as well as about7.5% of the nickel. The exit liquor contains about 90% of the nickel insolution and none of the cobalt. The mixed salt is recycled to theadjustment operation.

We claim:

l. A hydrometallurgical process for recovering a substantiallynickel-free cobalt product in the form of cobaltic hexammine sulfatefrom a solution comprising dissolved cobalt and nickel sulfatos whichcomprises: saturating said solution with ammonia so as to insureformation of the cobalt hexammine complex cation; adjusting the sulfateion concentration so as to satisfy the dissolved cobalt content in itstrivalent state and the dissolved nickel in its bivalent state;subjecting said solution at a temperature Vgreater than about F. and apressure at least equivalent to the vapor pressure of the solution tooxidation with a sulfur-free, oxygen-bearing oxidizing gas selected fromthe group consisting of oxygen, oxygen-enriched air and air, wherebydissolved cobalt is oxidized and a substantially nickel-free precipitateof cobaltic hexammine sulfate is obtained; and separating said cobaltichexammine sulfate precipitate. t

2. A hydrometallurgical process for recovering a substantiallynickel-free cobalt product in the form of co baltic hexammine sulfateand a substantially cobalt-free, nickel-bearing solution from a solutioncomprising dissolved cobalt and nickel sulfates which comprises:saturating the solution with ammonia to insure an ammonia to dissolvednickel plus cobalt mol ratio of from about 9:1 to about 15:1; adjustingthe sulfate ion concentration to satisfy the cobalt in its trivalentstate and the nickel in its bivalent state; subjecting the adjustedsolution at a temperature of 20D-350 F. and a pressure at leastequivalent to the vapor pressure of the solution to oxidation with asulfur-free, oxygen-bearing oxidizing gas selected from the groupconsisting of oxygen, oxygen-enriched air and air whereby dissolvedcobalt is oxidized and a substantially nickel-free precipitate ofcobaltic hexammine sulfate is obtained; separating and collecting saidprecipitate; saturating residual liquor with ammoniag'subjecting saidliquor at atemperature of 20C-350 F. and a pressure at leastequivalentto the vapor pressureof the solution to oxidation witha'sulfur-free, oxygen-bearing oxidizingV gas selected from the groupconsisting of oxygen, oxygen-enriched air and air whereby remainingcobalt is precipitated as a mixed cobalt-nickel product; and separatingsaid mixed metal precipitate leaving a substantially cobalt-free,nickel-bearing solution.

References Cited the le of this patent p UNITED STATES PATENTS 2,506,159

Mantell May 2, 1950 2,647,820 Forward Aug. 4, 1953 i FOREIGN PATENTS609,807 Great Britain Oct. 7, 1948 OTHER REFERENCES Mellor:Comprehensive Treatise on Inorganic and Theoretical Chemistry,publishedby Longmans, Green and Co., New York, 1935, vol. 14, page 790.

Grothe: Article on the separation of cobalt and nickel in the Germanpublication Metall und Erz, Number 22, Nov. 2, 1933, pages 449 to 455.

1. A HYDROMETALLURGICAL PROCESS FOR RECOVERING A SUBSTANTIALLYNICKEL-FREE COBALT PRODUCT IN THE FORM OF COBALTIC HEXAMMINE SULFATEFROM A SOLUTION COMPRISING DISSOLVED COBALT AND NICKEL SULFATES WHICHCOMPRISES: SATURATING SAID SOLUTION WITH AMMONIA SO AS TO INSUREFORMATION OF THE COBALT HEXAMMINE COMPLEX CATION; ADJUSTING THE SULFATEION CONCENTRATION SO AS TO SATISFY THE DISSOLVED COBALT CONTENT STATE;SUBJECTING SAID SOLUTION AT A TEMPERATURE GREATER THAN ABOUT 150* F. ANDA PRESSURE AT LEAST EQUIVALENT TO THE VAPOR PRESSURE OF THE SOLUTION TOOXIDATION WITH A SULFUR-FREE, OXYGEN-BEARING OXIDIZING GAS SELECTED FROMTHE GROUP CONSISTING OF OXYGEN, OXYGEN-ENRICHED AIR AND AIR, WHEREBYDISSOLVED COBALT IS OXIDIZED AND A SUBSTANTIALLY NICKEL-FREE PRECIPITATEOF COBALTIC HEXAMMINE SULFATE IS OBTAINED; AND SEPARATING SAID COBALTICHEXAMMINE SULFATE PRECIPITATE.